Many known prior art devices have been used to indicate brake wear on a braking mechanism, such as a pointer and a dial secured to a cam shaft and a lever, respectively. Attachment of this device was costly and could only be provided as original equipment. Timing of the pointer with the dial for a correct reading was difficult. Other indicators for brake wear are sensors and slack adjusters. Sensors are subject to failure and breakage. Slack adjusters can lose teeth and permit over travel of the push rod which in turn harms the braking mechanism.
Those concerned with these and other problems recognize the need for an improved air brake adjustment marker.